Adds oneshot layer and oneshot tap toggling (#308)

This commit is mostly a cherry-pick from `ahtn` at
https://github.com/tmk/tmk_keyboard/pull/255.

These are the changes:

* Adds ACTION_LAYER_ONESHOT
* Adds ONESHOT_TAP_TOGGLE
* Mentions sticky keys in the docs on oneshot.

1 files changed, 20 insertions, 0 deletions

diff --git a/tmk_core/common/action_util.h b/tmk_core/common/action_util.h
index 1a95cec10..dd0c4c2bf 100644
--- a/tmk_core/common/action_util.h
+++ b/tmk_core/common/action_util.h
@@ -56,10 +56,30 @@ void clear_macro_mods(void);
 
 /* oneshot modifier */
 void set_oneshot_mods(uint8_t mods);
+uint8_t get_oneshot_mods(void);
 void clear_oneshot_mods(void);
 void oneshot_toggle(void);
 void oneshot_enable(void);
 void oneshot_disable(void);
+bool has_oneshot_mods_timed_out(void);
+
+int8_t get_oneshot_locked_mods(void);
+void set_oneshot_locked_mods(int8_t mods);
+void clear_oneshot_locked_mods(void);
+
+typedef enum {
+  ONESHOT_PRESSED = 0b01,
+  ONESHOT_OTHER_KEY_PRESSED = 0b10,
+  ONESHOT_START = 0b11,
+  ONESHOT_TOGGLED = 0b100
+} oneshot_fullfillment_t;
+void set_oneshot_layer(uint8_t layer, uint8_t state);
+uint8_t get_oneshot_layer(void);
+void clear_oneshot_layer_state(oneshot_fullfillment_t state);
+void reset_oneshot_layer(void);
+bool is_oneshot_layer_active(void);
+uint8_t get_oneshot_layer_state(void);
+bool has_oneshot_layer_timed_out(void);
 
 /* inspect */
 uint8_t has_anykey(void);